PROCEEDINGS 



OF 



THE GEOLOGICAL SOCIETY OF LONDON. 



1831. No. 19. 



Jan. 5, 1831. — A paper was read entitled, " On the general struc- 

 ture of the Lake Mountains of the North of England, and on the 

 great dislocations by which they have been separated from the 

 neighbouring chains ;" by Prof. Sedgwick, M.A. Pres. G.S. F.R.S. 



The country, of which the author hopes to give a detailed descrip- 

 tion in a series of communications, is bounded to the west and the 

 south by the waters of the Irish Sea and Morecambe Bay. Towards 

 the north it descends into the plain of the new red sandstone within 

 the basin of the Eden ; and on the east side it presses against, and 

 partly encroaches on, the central carboniferous chain of the north. 

 Within these limits are found two distinct classes of rocks, all the cen- 

 tral region being composed of crystalline unstratified rocks, irregu- 

 larly associated with great formations of schist, which are subdivided 

 (agreeably to the system first published by Mr. Otley of Keswick,) 

 into three well defined groups ; while on the outskirts of these older 

 formations is a broken zone of carboniferous limestone, and exten- 

 sive deposits of superior [secondary] strata. The author avoids all 

 mineralogical details ; and after noticing the effects produced by the 

 several formations on the external features of the country, describes 

 at great length the range of a band of transition limestone (from 

 Millam in Cumberland, to the neighbourhood of Wasdale Head in 

 Westmoreland) nearly across the whole physical region under con- 

 sideration ; and states that it is finally cut off by a protruding boss 

 of granite, which he regards as newer than the limestone. Upon this 

 description he founds the following conclusions. 



1st. Great cracks and fissures were formed at a very ancient pe- 

 riod, diverging from the central regions, and intersecting the line 

 of bearing of the strata. All the great valleys in the range described, 

 are scooped out in the prolongation of these breaks, which were 

 in all cases accompanied with internal movements ; the present po- 

 sition of the systems of strata on the opposite sides of a transverse 

 valley sometimes indicating a relative lateral movement of more 

 than a mile in extent. These singular changes of position are re- 

 ferred partly to a true lateral shift, and partly to subsidence. 

 Reasoning from analogy, the author concludes that all the great 

 diverging valleys of the Lake Mountains took their origin in fissures 

 probably formed during the period of the protrusion of the central 

 syenite and granite. 



?ndly. He observes that the upper and lower systems of the slate 



